This invention relates to printers, in particular to paper trays of ink jet printers. In a convention ink jet printer, the output does not have a baking equipment to dry the printed ink for the sake of reduced cost and small size. As a result, if the drying speed of the ink on the output paper is slow, or if the solid area of a printed picture content is large, the following outputting paper may rub against the preceding paper to smear the undried printing.